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The disclosure relates to implantable medical devices (IMDs), and, more particularly, to detection of oversensed cardiac events by implantable medical devices.
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A variety of implantable medical devices (IMDs) for delivering a therapy have been clinically implanted or proposed for clinical implantation in patients. Some implantable medical devices may employ one or more elongated electrical leads carrying stimulation electrodes, sense electrodes, and/or other sensors. Implantable medical devices may deliver therapy or monitor conditions with respect to a variety of organs, nerves, muscle or tissue, such as the heart, brain, stomach, spinal cord, pelvic floor, or the like. Implantable medical leads may be configured to allow electrodes or other sensors to be positioned at desired locations for delivery of electrical stimulation or sensing of physiological conditions. For example, electrodes or sensors may be carried at a distal portion of a lead. A proximal portion of the lead may be coupled to an implantable medical device housing, which may contain circuitry such as signal generation circuitry and/or sensing circuitry.
Some IMDs, such as cardiac pacemakers or implantable cardioverter-defibrillators (ICDs), provide therapeutic electrical stimulation to the heart via electrodes carried by one or more implantable leads. The electrical stimulation may include signals such as pacing pulses, cardioversion shocks, or defibrillation shocks to address abnormal cardiac rhythms such as bradycardia, tachycardia, or fibrillation. In some cases, an IMD may sense intrinsic depolarizations of the heart to identify normal or abnormal rhythms. Upon detection of an abnormal rhythm, the device may deliver an appropriate electrical stimulation signal or signals to restore or maintain a more normal rhythm. For example, in some cases, an IMD may deliver pacing pulses to the heart upon detecting tachycardia or bradycardia, and deliver cardioversion or defibrillation shocks to the heart upon detecting tachycardia or fibrillation.
Leads associated with an IMD typically include a lead body containing one or more elongated electrical conductors that extend through the lead body from a connector assembly provided at a proximal lead end to one or more electrodes located at the distal lead end or elsewhere along the length of the lead body. The conductors connect stimulation and/or sensing circuitry within an associated IMD housing to respective electrodes or sensors. Some electrodes may be used for both stimulation and sensing, while other electrodes may be dedicated to only stimulation or only sensing. Each electrical conductor is typically electrically isolated from other electrical conductors, and is encased within an outer sheath that electrically insulates the lead conductors from body tissue and fluids.
Cardiac lead bodies tend to be continuously flexed by the beating of the heart. Other stresses may be applied to the lead body during implantation or lead repositioning. Patient movement can cause the route traversed by the lead body to be constricted or otherwise altered, causing stresses on the lead body. The electrical connection between implantable medical device connector elements and the lead connector elements can be intermittently or continuously disrupted. Connection mechanisms, such as set screws, may be insufficiently tightened at the time of implantation, followed by a gradual loosening of the connection. Also, lead pins may not be completely inserted. In some cases, changes in leads or connections may result in intermittent or continuous changes in lead impedance.
Short circuits, open circuits or significant changes in impedance may be referred to, in general, as lead-related conditions. In the case of cardiac leads, sensing of an intrinsic heart rhythm through a lead can be altered by lead-related conditions. Structural modifications to leads, conductors or electrodes may alter sensing integrity. Furthermore, impedance changes in the stimulation path due to lead-related conditions may affect sensing and stimulation integrity for pacing, cardioversion, or defibrillation. In addition to lead-related conditions, conditions associated with sensor devices or sensing circuitry, as well as conditions associated with electrodes or sensors not located on leads, may affect sensing integrity. Lead-related conditions, electromagnetic interference (EMI), myopotentials caused by patient movement, or other noise sources may affect sensing integrity. Cardiac events that are falsely detected may be referred to as oversensed cardiac events.
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In general, the disclosure is directed to techniques for identification and remediation of oversensed cardiac events in an IMD. The techniques may make use of far-field electrograms (FFEGMs) to identify oversensed cardiac events. Identification of oversensed cardiac events can be used in an IMD to prevent inappropriate ventricular fibrillation (VF) detection, and thereby avoid delivery of an unnecessary defibrillation shock. Alternatively, or additionally, identification of oversensed cardiac events can be used in an IMD to support delivery of bradycardia pacing during an oversensing condition. In some cases, bradycardia pacing delivered in response to detection of oversensed cardiac events may include pacing pulses from multiple stimulation vectors to provide redundancy in the event the oversensing may be due to a lead-related condition. The techniques, in some cases, may repair interval data upon identification of oversensing to support proper operation of defibrillation and/or pacing therapies that are responsive to the interval data.
In one example, the disclosure provides a method comprising acquiring a first cardiac signal via a first sense electrode configuration, acquiring a second cardiac signal via a second sense electrode configuration, detecting cardiac events in the first cardiac signal, identifying at least some of the cardiac events detected in the first cardiac signal as oversensed events based on whether one or more characteristics of the second cardiac signal confirm the cardiac events, and controlling delivery of cardiac electrical stimulation therapy to a patient based on the identification of the oversensed events.
In another example, the disclosure provides an implantable medical device comprising an electrical sensing module configured to acquire first cardiac signal via a first sense electrode configuration, and acquire a second cardiac signal via a second sense electrode configuration, a stimulation module configured to deliver cardiac electrical stimulation therapy to a patient via stimulation electrodes, and a processor configured to detect cardiac events in the first cardiac signal, identify at least some of the cardiac events detected in the first cardiac signal as oversensed events based on whether one or more characteristics of the second cardiac signal confirm the cardiac events, and control the stimulation module to deliver the cardiac electrical stimulation therapy to the patient based on the identification of the oversensed events.
In another example, the disclosure provides a computer-readable storage medium comprising instructions that, when executed by a processor in an implantable medical device, cause the processor to detect cardiac events in a first cardiac signal acquired via a first sense electrode configuration, identify at least some of the cardiac events detected in the first cardiac signal as oversensed events based on whether one or more characteristics of a second cardiac signal acquired via a second sense electrode configuration confirm the cardiac events, and control a stimulation module to deliver of cardiac electrical stimulation therapy to a patient based on the identification of the oversensed events.
The details of one or more aspects of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
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FIG. 1 is a conceptual diagram illustrating a therapy system comprising an implantable medical device (IMD) in the form of an implantable cardioverter defibrillator (ICD) for delivering stimulation therapy to a heart of a patient via implantable leads.
FIG. 2 is a conceptual diagram further illustrating the ICD and leads of the system of FIG. 1 in conjunction with the heart.
FIG. 3 is a conceptual diagram illustrating another example therapy system comprising the ICD of FIG. 1 coupled to a different configuration of leads.
FIG. 4 is a functional block diagram illustrating example components of the ICD of FIG. 1.
FIG. 5 is a functional block diagram illustrating an example electrical sensing module of the ICD of FIG. 1.
FIG. 6 is a flow diagram illustrating a method for identification and remediation of oversensed cardiac event.
FIG. 7 is a flow diagram illustrating an example of the use of far-field electrogram (FFEGM) amplitude analysis in the method of FIG. 6.
FIG. 8 is a graph illustrating a technique for identification and remediation of oversensed cardiac events using an FFEGM to inhibit delivery of an inappropriate defibrillation shock.
FIG. 9 is a graph illustrating a technique for identification and remediation of oversensed cardiac events using an FFEGM to permit delivery of a bradycardia pacing pulse.
FIG. 10 is a graph illustrating another technique for identification and remediation of oversensed cardiac events using an FFEGM to permit delivery of a bradycardia pacing pulse and immediate backup pacing pulse.
FIG. 11 is a graph illustrating an additional technique for identification and remediation of oversensed cardiac events using an FFEGM to permit delivery of a bradycardia pacing pulse and immediate backup pacing pulse.
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In general, the disclosure is directed to techniques for identification and remediation of oversensed cardiac events using far-field electrograms (FFEGMs). Lead-related conditions (e.g. fracture, insulation breach, loose set screw, or the like), EMI, myopotentials, or other noise sources may produce noise that causes oversensing of cardiac events, i.e., false detection of cardiac events. Oversensing of cardiac events due to noise can affect the operation of an IMD such as an implantable cardioverter defibrillator (ICD).
An oversensed event may refer, generally, to any cardiac event that is falsely detected due to any of a variety of factors, such as the noise sources described above. The oversensed event does not generally represent an actual physiological event within the heart, such as a ventricular depolarization (R wave), but instead an artifact of a noise source, such as a fractured conductor in a lead or some other lead-related condition. In contrast, a valid, detected cardiac event will be based on signal characteristics consistent with an actual physiological activity of the heart.
Oversensing may cause an implantable cardioverter defibrillator (ICD) or other IMD to deliver inappropriate cardioversion or defibrillation shocks. In particular, oversensing may result in an erroneous indication of arrhythmia, causing the ICD to deliver an unnecessary shock. Unnecessary shocks can be painful, potentially pro-arrhythmic, and consume excessive amounts of power from finite battery resources.
In addition, in an ICD, oversensing may cause syncope and asystole in pacemaker-dependent patients. Increased numbers of pacemaker-dependent patients are receiving ICDs, including Cardiac Resynchronization Therapy (CRT) devices. Oversensing may cause bradycardia pacing to be inhibited due to an erroneous indication of arrhythmia. For example, during a detected arrhythmia, the ICD may inhibit pacing to avoid affecting detection of ventricular fibrillation, or to avoid the possibility of pacing the patient into ventricular fibrillation.
Also, if the noise source is a fractured lead, in addition to causing oversensing, there may be an added risk of failure to capture the heart with a pacing pulse due to a compromised conductor. In this case, even if pacing is not inhibited, syncope and asystole may still be a concern if the same conductor used to sense cardiac events is also used to deliver cardioversion, defibrillation or pacing therapy to the patient.